1. Field of the Invention
The present invention relates to a camera having focus detection means and visual axis detection means, and more particularly to a camera, such as a photographing camera, a video camera, an SV camera, etc., in which the visual axis detection means detects a direction of a visual axis of an observer looking into a viewfinder, to thereby determine a targeting direction and a targeting spot in the finder view. The focus detection means has a function of detecting in-focus states in a plurality of areas based on signals obtained by the visual axis detection means, and one of plural in-focus signals obtained by the focus detection means is selected to adjust the in-focus state of a photographing system.
2. Related Background Art
There have heretofore been proposed a variety of cameras in which visual axis detection means provided in the camera senses a direction of the visual axis of a photographer to detect an area (position) in a viewfinder which the photographer is observing, i.e., a so-called targeting direction of the photographer, and various photographing functions such as automatic focus adjustment and automatic exposure setting are controlled in response to a signal from the visual axis detection means.
Japanese Patent Laid-Open No. 61-61135 and U.S. Pat. No. 4,574,314, for example, propose a camera wherein the distance measuring direction of a focus detector is mechanically controlled in response to an output signal from the visual axis detection means, for adjusting the in-focus state of a photographing system.
The assignee of the present application has proposed, in Japanese Patent Laid-Open No. 1-241511, a camera which comprises visual axis detection means for detecting a targeting direction of a potographer, focus detection means having a plurality of distance measuring views, and automatic exposure control means having plural distribution patterns of light measuring sensitivity, whereby driving of the focus detection means and the automatic exposure control means are controlled in response to an output signal from the visual axis detection means.
While photographing conditions such as focus adjustment and exposure control have been automatically set in a prior camera by using a central area of the viewfinder as a reference, the camera proposed in the above Japanese Patent Laid-Open No. 1-241511 enables the photographer to select an arbitrary area (or multiple areas in some cases) within the viewfinder at his or her discretion for carrying out the focus adjustment, the exposure control, etc. based on the selected area. Accordingly, a photo can be taken under free conditions intended by the photographer, apart from a method of automatically controlling the composition which is the most important factor in photographing.
The automatic focus detecting technique conventionally used in cameras are divided into two main categories; a passive type that utilizes natural light coming from an object, and an active type that projects a light beam to an object from the camera and utilizes the reflected light from the object.
The passive type technique further includes a contrast detection type that measures sharpness of an object image, and a correlation type that photoelectrically detects a match of a double object image based on the principles of triangulation. In any of passive type techniques, a distribution pattern of the light intensity over the object surface is measured and an image analysis is carried out from the measured result for focus detection. Accordingly, if the object has extremely low brightness or extremely low contrast, there cannot be obtained a satisfactory distribution pattern of the light intensity as a basis for the image analysis, resulting in the focus detection failing to operate or the detecting accuracy being reduced.
On the other hand, the active type technique also has a problem in that the focus detection fails to operate or the detecting accuracy is reduced for the following reasons:
(A) If the object surface has low reflectance, the reflected light intensity is too low; PA0 (B) If any object of high brightness exists in the surroundings, it becomes difficult to discriminate the reflected component of the projected light from the object; and PA0 (C) If the distance to the object is long, the reflected component of the projected light is reduced.
Thus, any of the focus detection techniques has suffered from the problem that the focus detection may fail to operate or the detecting accuracy may be reduce.
Accordingly, even if a focus detection area (distance measuring point) is set based on a signal corresponding to the targeting direction of the photographer (the signal being obtained by the visual axis detection means provided on a camera), an infocus signal for that area cannot be produced or, otherwise, is produced with low reliability depending on the circumstances.
Another problem is that in the case of automatic focus detection, the detection is disabled, or, in the case of an object pattern which causes substantial detection errors, an infocus signal cannot be obtained when the targeting direction of the photographer is put toward such an object.
Meanwhile, as regards the visual axis detection means, a photographer usually tends to look at the background or surrounding objects as well as the main object to be photographed. For this reason, the true targeting direction (targeting spot) must be identified from a motion of the visual axis direction of the photographer over time. However, the detection of the visual axis becomes difficult depending on motions of the visual axis, and the detection accuracy of the visual axis is lowered under the presence of strong images or noise due to extraneous light in a detection optical system. This makes it very difficult to detect the targeting direction in the viewfinder from the direction of visual axis of the photographer.
On the other hand, automatic focus detection means in recent cameras has a frame area for distance measurement which does not always cover the entire frame to be photographed, and sets a plurality of distance measuring fields of view in a part of the photographed frame in many cases. Stated otherwise, because a main object is seldom located in an edge of the frame, an automatic focus detection area is set in a central region of the frame, excepting four corners thereof, in area proportion of approximately 1/10 to 1/2 for the entire frame.
In a camera thus constituted, if the targeting direction of a photographer is outside the focus detection area, the focus detection cannot be effected.
Where the distance measuring fields of view are apart from one another, such a failure also occurs in an intermediate area between the fields of view.
Moreover, conventional cameras are designed to simply move an object area for the automatic focus detection depending on a motion of the visual axis direction of a photographer. No considerations have so far been paid to the ability to cope with the event that the focus detection means and/or the visual axis detection means partially fails to detect, or wherein a mismatch occurs in the process of control.
Accordingly, even those cameras which include the focus detection means and the visual axis detection means have produced problems wherein desired functions of such cameras cannot be fully effected in some cases.